In a vibration-type angular velocity sensor, an oscillator vibrates in a predetermined direction (hereinafter called a “drive direction”). When angular velocity about an axis perpendicular to the drive direction is applied to the oscillator, Coriolis force proportional to the applied angular velocity is generated in a direction (hereinafter called a “detection direction”) perpendicular to each of the drive direction and the axis. The angular velocity is measured by detecting the Coriolis force.
In one method of detecting the Coriolis force, the Coriolis force is detected as inertial force. That is, in the method, a weight member movable in the detection direction is used, and the Coriolis force is detected by detecting the amount of displacement of the weight member caused by the Coriolis force.
It is noted that the weight member can be displaced in the detection direction even when acceleration unrelated to the Coriolis force is applied to the weight member. Therefore, to calculate the angular velocity from the Coriolis force, the displacement caused by the Coriolis force needs to be separated from the displacement caused by the acceleration.
U.S. Pat. No. 5,604,312 corresponding to JP-A-2007-101553 discloses a technique for separating the displacement caused by the Coriolis force from the displacement caused by the acceleration to detect the displacement caused by the Coriolis force. In a vibration-type angular velocity sensor disclosed in U.S. Pat. No. 5,604,312, two oscillators are mechanically coupled together by a spring-shaped beam (hereinafter called a “coupling beam”) that is soft in the drive direction. The oscillators are driven to vibrate at the same frequency but in opposite phase. A detection weight movable in the detection direction is provided inside each oscillator and connected to the oscillator. Thus, while the oscillator vibrates and is displaced in the drive direction, the detection weight is displaced in the drive direction with vibration of the oscillator and also displaced in the detection direction according to the Coriolis force.
The vibration-type angular velocity sensor disclosed in U.S. Pat. No. 5,604,312 uses the principal that the amount of displacement of the detection weight due to the Coriolis force is proportional to the angular velocity applied to the detection weight and the vibration speed of the detection weight in the drive direction. In the vibration-type angular velocity sensor, since the two oscillators vibrate in opposite directions (i.e., in opposite phase), the two detection weights are displaced in opposite directions according to the applied angular velocity. In this way, by causing the two oscillators to vibrate in opposite phase, the Coriolis forces are generated at the two detection weights in opposite phase synchronously with the drive frequency. It is noted that when acceleration is applied in the detection direction, the two detection weights are displaced in the drive direction by the same amount regardless of the drive frequency. Therefore, in the vibration-type angular velocity sensor, the displacement caused by the Coriolis force is separated from the displacement caused by the acceleration by sampling a difference between the amounts of displacement of the two oscillators in the detection direction.
According to the vibration-type angular velocity sensor disclosed in U.S. Pat. No. 5,604,312, the two oscillators are flat-shaped oscillators made of a silicon substrate. Further, the coupling beam for coupling the two oscillators are made of the silicon substrate and formed at the same layer as the two oscillators.
Since the oscillators and the coupling beam are formed at the same layer of a silicon substrate, other functional portions such as drive electrodes and additional coupling beams cannot be formed between the oscillators.